This invention relates to electrical circuitry for surge suppression and rectification.
It is well known to employ two Zener diodes with one pair of common electrodes connected together as a voltage surge suppressor for protecting some circuitry from excessive AC voltages. As so connected, the Zener diodes are said to be in series opposition. When connected across the input terminals of a circuit portion to be protected they act, together, as practically an open circuit unless and until the AC voltage exceeds the Zener breakdown voltage of the diodes.
One instance in which Zener diode voltage suppressors are used in the foregoing manner is where a component, such as thyristor, must be protected from large forward and reverse transients in order to avoid damage to it. For example, this is the case in ground fault interrupters having a sense amplifier and trip circuit energized by the line voltage and employing a thyristor in a manner such as that described in copending application Ser. No. 302,949, filed Nov. 1, 1972 by the present inventor and others now U.S. Pat. No. 3,852,642 issued Dec. 3, 1974. A straightforward application of a Zener diode voltage suppressor for the protection of a thyristor in such a circuit requires the addition of two components, namely the two Zener diodes, with the disadvantages of their cost and inherent size. It is the case in ground fault interrupters, as it is in many other types of circuits, that the number, cost, and size of components must be minimized to achieve a commercially successful product yet without detracting from the functioning of the circuit.